Electrical logging of well bores



March 13, 1945.

A. L. SMITH ELECTRICAL LOGGING OF WELL BORES Filed July 29, 1940 jENEEATOE. SOUQCE V M0702 OFWAZL 5A MPll/VG DEV/CE A LONZO L. SMITH A TTORNEYE however, obscured by electrical sm st, p

1 'EwcmcAL LOGGING or WELL norms Alonso L. Smith, Houston, Tex. assionately 29, 194b, Serial No. 348,117

' 3 Claims. (01. 175-182) This invention relates to improved means and method for electrically logging well bores.

In the log ing of well bores it has been proposed to lower one or more electrodes within the liquid in the well bore and to apply an electrical potential between an electrode and the earth or between; spaced electrodes to establish a localized area of.

.current conduction within the formations of which information is desired. As thi area of current conductionis made to traverse the bore 10 hole observations are made of the resistivity of the surrounding formations by measuring the fluctuation in the current or potential within the area, such fluctuations being due to the change in electrical characteristics of the formations and 15 hence serving as an indication of the nature of the formations, particularly as regards potential horizons for the production of oil and gas.

The results obtained by prior practices are,

by earth which may be telluric in nature or merely induced strays, such currents introduc ing spurious indications as to the nature oi'the formations traversed by the bore hole. Furthermore, thedistribution of current resulting from V the applied potential may assume such proportions that the definition both as to the nature and extent of the formations is indistinct. a

The primary object of the invention is to provide new and improved method and apparatus for logging well bores in a manner that the'above indicated dimculties will be avoided.

1 more specificv object of the invention is to create a localised current condition in and about is i v A further object is to provide electricslwell 88 8 apparatus which is little ailected liy temperature changes within the well bore.

a further object is is electrically log wen bores by utilisation of whereby the streets of iortuitous stray currents are Still is to iosawell hole by low, ering. thereina bare and current carryin; resistor so that the voltage drop in such resistor eunmt stterminuie liquidin" the wellbore and the formations so that variatims in theapparent resistanceoi the resistor proridesnindlcation'as tothe nature of" 50 Still to. provide well logging i apparatus which is capable of performing addiwithin the well bore.

'Ihefotmobiechtosetherwith o hercc ieetswillbefurtherawarentfromiheiollowins polarization and the well bore-in such a manner that polarization minimised.

description taken in connection with the accompanying drawing in which:

Fig. l is a sectional view through a bore hole and includes an illustrative embodiment of appsratus of the invention;

. Fig. 2 isa diagrammatic illustration of a log-, ging unit adapted to procure a sample in the well.

the bore hole I passes from the surface 2 of the earth thru the overburden: and the subiacent earth formations l to I inclusive. The principal object of the invention is that of determining the nature and extent of the respective formations I to 8, particularly as regards potential productivity of oil or gas or other valuable sub- I surface materials.

The bore hole I is usually partly or entirely filled with a liquid it which is electrically conductive and into which, in accordance with the invention, is lowered the elongated resistor II.

The terminals of this resistor are connected to the ends of a conductor cable having insulated wires l2 and" which are interconnected thru a double-pole double-throw switch II and an electrical instrument It by means of which it is possible to obtain an indication or record of the electrical conditions within the well as the resistor I l is moved axially thereof.

Attention is directed to the iact that a certain amountof stratiflcation may take place in the liquid il wihinthe well. In such case it is desirable, though not essential, that a preliminary agitating step be taken in order that this liquid may be relatively homogeneous when a log of. the well bore is to betaken.

Connected to the terminals 28 of the doublepole double-throw switch It is a source of electrical energy such source being, shown as a battery II. The other terminals 25 of the switch are connected to a second source II of electrical energy of larger capacity to serve a' purpose that will he more fully described.'

The resistor ll may be made of any suitable material but preferably comprises a material havlog a relatively low temperature coeilicient of resistance such as eonstantan or manganin, -etc..' so that circuit conditions'will be inappreciably modified hytemperatu're changes and particularly the changes ofthe magnitudes which are encountered in extremely deep wells. This resistance is preferably of much greater length than the diameter of the bore hole and in fact if the both is.

say nine andsev'en-eighths inches in diameter.

the resistor may b three to tenfeet in-iength. u The resistance of such element would, oi

depend the conductivity of the fluid and appliedtotheenchaotthereaistorfiomthemeer ll will causefa cnrxentto'iiow thru: the resistor and also throughout-an area indicated lladjaemt-theteto inthefonnatim It is; to he noted that the current pattem'fl e!- tendabeyondthehoreholeandpasses'thrmnh the surrounding earth formations so that the 4 pattern. will with the variations in. the. eleccharacteristics: of the formations such as to inclusive; In as much. as; all other charactertiscs are eonstantthevariati'onsin. the formations may be readily the liquid II in; homogeneous, a condition; whichmay'he by the technique above set:- forth, the: resistance to the flow of current I the resistor [I and the liquid II is substantially constant. The total flow of current, however; on the: apparentresistance of the resistor "I will vary as the: electrical. characteristics-oi the formations: vary. These variations maybe determinedinanyofvarions ways. For example the instalment I! may comprise an whereby the apparent on elective resistance of the restistor I I is measured Alternativek the potential applied by the source 21 may be maintained constant as indicated by the voltmeter liandan ammetermayheutiliaedasthe instrument II. It-is oteonrseunderstood that the instrument med maybe oi either theindicatin: type or the recotdinl type as desired.

Itahould aiao henotedthatthecurrentflowin: thmtheelectriceizeuitmas bemaintained eonatantby vaninlthevoltagesnppliedtothe terannals 1| 0! the: switch ll. Under such circumstanoes the variations in the applied potential wilibeindieatedotreeotdedtopmvidethe necessary information whereby the electrical characteristics of the geoloaical formations are deter- Anctherieatmeoiftheimentionresidesmthe factthatthereaiatot ll isaoeonstmctedthata suitahieoverioadmayhe applied withmxtinjur! shownaseomprtsineahotginc aiotthemofln'fl trlmnandmtint maehanimfoeadvaneinaandretraetinaaedee banelflnherebythededredaampleoraamplea mau'hetahmnhmthenitchlliathmmto maybe ,cloeedupontemmaleltatanehtimeuis deemed dairable to begin. observations. The

linctuatimle: of resistivity of the formations will.

' ,otthevariouesuhmdaeetormations and the leveleat these. tomatiom occur.

1.: m nxethod ot detennininl the nature of geological strata penetrated by a bore hole com- I prising the step: of, ttaversinl the liquid within hole with a bare resistor of a high resiatanee material, having a low tenmeratme eohmmmmem-aotaw reautaneematedalhaflnlalowtunpetanneeoemcientofxeaktmappblfltaneleetricaiw tuitiaitoaaidenmmetonmthemonthotthe step 3.Anapparatmforlouinawelibomeo|npdsinmahareresiatnnaaiizmbeinaotahiah redatancematerialhavinealowtemperatweeoancient of renatanee, insulated eonductors attaehedtotheenda'thetedandaxhptedtolover thereslstorwithinawelihoteameeotelecammonium-n. 

